Presentation Slides for Air Pollution and Global Warming:
History, Science, and Solutions Chapter 7: Effects of Pollution on Visibility, UV
Radiation, and Colors in the Sky
By Mark Z. JacobsonCambridge University Press (2012)
Last update: February 8, 2012
The photographs shown here either appear in the textbook or were obtained from the internet and are provided to facilitate their display during course instruction. Permissions for publication of photographs must be requested from individual
copyright holders. The source of each photograph is given below the figure and/or in the back of the textbook.
Additive Colors
www.wiu.edu; theaudacityofcolor.com
0.38-0.5 micron
0.6-0.75 micron
0.5-0.6 micron
Artist’s primaries
Newton’s primaries
Light Attenuation ProcessesGas absorption
Gas scattering
Aerosol and hydrometeor particle absorption
Aerosol and hydrometeor particle scatteringReflectionRefractionDispersionDiffraction
Light-Absorbing GasesGas Absorption wavelengths (um)
Visible/Near-UV/Far-UV absorbersOzone < 0.35, 0.45-0.75Nitrate radical < 0.67Nitrogen dioxide < 0.71
Near-UV/Far-UV absorbersFormaldehyde < 0.36Nitric acid < 0.33
Far-UV absorbersMolecular oxygen < 0.245Carbon dioxide < 0.21Water vapor < 0.21Molecular nitrogen < 0.1
Gas Absorption
Attenuation of light intensity
(7.2)
Absorption extinction coefficient (1/cm)
(7.1)
b = gas absorption cross section (cm2/molec.)
N = gas concentration (molec./cm3)
Conversion of radiative energy to internal energy by a gas molecule, increasing the temperature of the molecule
Absorption Extinction Coefficients of Nitrogen Dioxide and Ozone
Figure 7.3
openlearn.open.ac.uk
NO2
J. Lew
Purple Sky Due to Ozone Absorption of Green Light After El Chichon
Volcano, 1982
Northumberland, UKIan Britton
Red Sunrise / Purple Sky
Why is the Sky Blue?
liamdaly.com
Gas (Rayleigh) ScatteringRedirection of radiation by a gas molecule without a net
transfer of energy to the molecule
Probability distribution of where a gas molecule scatters incoming light
Figure 7.4
Color of the Sky and Sun
Figure 7.6
Sun at Noon and in the Afternoon
liamdaly.com I146.photobucket.com
Yellowsunset
Yellow Sun at SunsetMark Z. Jacobson
Red Horizon Over Clouds During Sunset
Mark Z. Jacobson
Red Sun Through Pollution
molvray.com Intlxpatr.files.wordpress.com
Red Sky Due to Smog(Salton Sea, California)
Charles O'Rear, U.S. EPA, May, 1972, Still Pictures Branch, U.S. National Archives
Particle Absorption
Attenuation of light through particle
(7.4)
Conversion of radiative energy to internal energy by a particle, increasing the temperature of the particle
Effects of Pollution on UV Radiation Reaching Surface
Figure 7.12
Imaginary Refractive Indices of Organic and Black Carbon
Figure 7.11
Tarballs
Adachi and Buseck (2011)
Brown Particles in Los Angeles Smog(Dec. 2000)
Mark Z. Jacobson
Brown Color of Nitrogen Dioxide and Organic Particles
From preferential absorption of blue and some green by particles and transmission of red and remaining green (which makes brown)
Visible
Infrared
Black Carbon and Soot
img.alibaba.comwww.ecofuss.com
Black Color of Soot
Soot appears black because it absorbs all visible wavelengths (blue, green, red) and transmits no light. Infrared
Visible
Particle ScatteringReflection
The bounceoff of light from an object at the angle of incidence Refraction
Bending of light as it travels between media of different densityDispersion
Separation of white light into colorsDiffraction
Bending of light around objectsScattering
Combination of reflection, refraction, dispersion, diffraction.The deflection of light in random directions.
Reflection and Refraction
Snell’s Law
(7.5)
Real part of refractive index
n1= c/c1 (7.6)
c = speed of light in vacuum
Refraction of Starlight
Figure 7.14
Diffraction Around A Particle
Figure 7.15
Huygens' principle
Each point of an advancing wavefront may be considered the source of a new series of secondary waves
Huygen’s Principle
www.sgha.net
Every point on a wave front can be considered as a source of wavelets that spread out in the forward direction at the speed of the wave itself.
Upload.wikimedia.org
Radiation Scattering by a Sphere
Figure 7.16
Ray A is reflectedRay B is refracted twiceRay C is diffractedRay D is refracted, reflected twice, then refractedRay E is refracted, reflected once, and refracted
Geometry of a Primary Rainbow
Figure 7.19
Primary Rainbow
Commander John Bortniak, NOAA Corps, available from the National Oceanic and Atmospheric Administration Central Library
Forward Scattering of Sunlight
Mark Z. Jacobson
Soot Absorption/Scattering Efficiencies
Fig. 7.20
Single soot particle absorption/scattering efficiencies and forward scattering efficiencies at a wavelength of 0.50 micron
Water Absorption/Scattering Efficiencies
Figure 7.21
Single water particle absorption/scattering efficiencies and forward scattering efficiencies at a wavelength of 0.50 micron
Los Angeles Haze
Gene Daniels, U.S. EPA, May, 1972, Still Pictures Branch, U.S. National Archives
Haze and Fog Over Los Angeles
Gene Daniels, U.S. EPA, May, 1972, Still Pictures Branch, U.S. National Archives
Visibility DefinitionsMeteorological range
Distance from an ideal dark object at which the object has a 0.02 liminal contrast ratio against a white background
Liminal contrast ratioLowest visually perceptible brightness contrast a person can see
Visual rangeActual distance at which a person can discern an ideal dark object against the horizon sky
Prevailing visibilityGreatest visual range a person can see along 50 percent or more of the horizon circle (360o), but not necessarily in continuous sectors around the circle.
VisibilityThe intensity of radiation increases from 0 at point x0 to I at point x due to the scattering of background light into the viewer’s path
Figure 7.22
Meteorological RangeChange in object intensity along path of radiation (7.9)
Total extinction coefficient (7.10)
dIdx
=σt IB −I( )
σt=σa,g+σs,g+σa,p+σs,p
Integrate (7.9) (7.11)
Define liminal contrast ratio --> meteorological range (7.12)
IB−IIB
=e−σtx
Cratio=IB −IIB
=0.02 → x=3.912σt
Meteorological Range
(Larson et al., 1984)Table 7.4
Meteorological Range (km)
Gas scattering
Gas absorption
Particle scattering
Particle absorption
All
Polluted day
366 130 9.59 49.7 7.42
Less-polluted
day
352 326 151 421 67.1
Winter and Summer Maps of Light Extinction
Schichtel et al. (2001)